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req fuel setting Microsquirt/Tuner studio

redleg

New member
Joined
Dec 26, 2012
Location
Orlando
Removed my 700cc injectors replaced with 1000cc injectors. Increase of 30%. Required fuel was @5.6ms with the 700cc's. Thought I would need to reduced the req fuel by 30%. Fuel calculator gave me 3.9ms, however car would not start. I increased req fuel to 10.0ms car fired up after some cranking pulse tweaking. Why am I having to increase the req.fuel with the 1000cc injectors? I thought I would be decreasing that value. Originally with the 700cc inj. my ve @ idle 48kpa/900rpm was set to 90 in that cell. Now with 1000cc injectors my value is 68 @ 48kpa/900rpm around 14.5 AFR, little more head room.Anyone know why I needed to increase the req fuel with the larger injectors? Seems backwards to me..

Thanks.
 
Some injectors like different base pressures. I wouldn't pay too much attention to it, put whatever value there it takes to get it running right and tune from there.
 
yeah, swapping injectors and changing the req fuel to cover for it only sorta works. If you have all the low pw non linear stuff plugged in it probably works better, but for most people, your idle PW doesn't change much from a 600 to say a 1300cc injector. Where it changes a lot is generally past the 2.5ms range. You will likely find that you can reduce your in boost above 2000rpms bins by close to the % difference if not a little more, but down around idle don't expect it to change a whole lot.
 
Removed my 700cc injectors replaced with 1000cc injectors. Increase of 30%. Required fuel was @5.6ms with the 700cc's. Thought I would need to reduced the req fuel by 30%. Fuel calculator gave me 3.9ms, however car would not start. I increased req fuel to 10.0ms car fired up after some cranking pulse tweaking. Why am I having to increase the req.fuel with the 1000cc injectors? I thought I would be decreasing that value. Originally with the 700cc inj. my ve @ idle 48kpa/900rpm was set to 90 in that cell. Now with 1000cc injectors my value is 68 @ 48kpa/900rpm around 14.5 AFR, little more head room.Anyone know why I needed to increase the req fuel with the larger injectors? Seems backwards to me..

Thanks.

Since you are talking Required Fuel, I am guessing that this is a Megasquirt application? 1000cc/700cc = 1.43, a 43 % increase in fuel flow rate. 5.6 ms/1.43 = 3.9 ms. The Req fuel calculator in Tuner Studio is working just fine and you need to polish up your math skills a bit.

If your configuration in Tuner Studio is correct, you can alter the size of your injectors, recalculate and apply the new value of Req Fuel, change the injector opening times and voltage sensitivity to match the new injectors and within reason you should not need to make any other changes to the Tuner Studio configuration settings. If the injector flow rates, injector opening times and voltage sensitivities were correct for both the 700 cc injectors and the 1000 cc injectors then you should not have to alter the other configuration settings. If you had errors in your original injector data then your other Tuner Studio settings will have been adjusted to make up for those errors. As such, even if you have correct data for the 1000 cc injectors you are putting them into a fudged configuration and you are starting all over. Same if you don't have correct data for the 1000 cc injectors.

Increasing the Req Fuel to 10.0 ms has the effect (everything else being unchanged) of reducing the calculated fuel pulse width. If you needed to increase Req Fuel / reduce your calculated fuel pulse width to get the car started, I am guessing that you were applying too much fuel during cranking with your original settings. Have you been logging any of these starts. Do you know what your cranking PW values were before you did the injector change and what they were after?

Putting in larger injectors increases the sensitivity to correct injector opening time and voltage sensitivity. If you have an error in the calculated fuel pulse width at idle because of incorrect injector opening time you have potentialy increased the magnitude of the error by 43 % with your new injectors. If you want the engine to start and idle well with large injectors you absolutely have to have the correct values for open time and voltage sensitivity for the injectors.

A Ve value of 90 in an idle cell in the fuel map is really odd. My car runs Ve values around 48 in the idle cells (MAP around 55, RPM 900) and if you use any of those generic Ve table generators you will typically get Ve values in the 40 - 50 range. This suggests to me that your configuration in Tuner Studio is off.
 
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What size injectors are you running? And what's your PW @ idle? Never had issues starting hot or cold with the 700cc's.
700cc's Cranking PW are:
60degrees@275,85degress@260, 105@180,130@145,150@125,160@115,180@98,190@96,
215@90.

Since you are talking Required Fuel, I am guessing that this is a Megasquirt application? 1000cc/700cc = 1.43, a 43 % increase in fuel flow rate. 5.6 ms/1.43 = 3.9 ms. The Req fuel calculator in Tuner Studio is working just fine and you need to polish up your math skills a bit.

If your configuration in Tuner Studio is correct, you can alter the size of your injectors, recalculate and apply the new value of Req Fuel, change the injector opening times and voltage sensitivity to match the new injectors and within reason you should not need to make any other changes to the Tuner Studio configuration settings. If the injector flow rates, injector opening times and voltage sensitivities were correct for both the 700 cc injectors and the 1000 cc injectors then you should not have to alter the other configuration settings. If you had errors in your original injector data then your other Tuner Studio settings will have been adjusted to make up for those errors. As such, even if you have correct data for the 1000 cc injectors you are putting them into a fudged configuration and you are starting all over. Same if you don't have correct data for the 1000 cc injectors.

Increasing the Req Fuel to 10.0 ms has the effect (everything else being unchanged) of reducing the calculated fuel pulse width. If you needed to increase Req Fuel / reduce your calculated fuel pulse width to get the car started, I am guessing that you were applying too much fuel during cranking with your original settings. Have you been logging any of these starts. Do you know what your cranking PW values were before you did the injector change and what they were after?

Putting in larger injectors increases the sensitivity to correct injector opening time and voltage sensitivity. If you have an error in the calculated fuel pulse width at idle because of incorrect injector opening time you have potentialy increased the magnitude of the error by 43 % with your new injectors. If you want the engine to start and idle well with large injectors you absolutely have to have the correct values for open time and voltage sensitivity for the injectors.

A Ve value of 90 in an idle cell in the fuel map is really odd. My car runs Ve values around 48 in the idle cells (MAP around 55, RPM 900) and if you use any of those generic Ve table generators you will typically get Ve values in the 40 - 50 range. This suggests to me that your configuration in Tuner Studio is off.
 
My PW with the 700cc's is 3.1ms at idle. It was 4.2ms at idle with the 1000cc's. It drove alright but idled like crap. I bailed on the 1000cc's and put back in the 700cc's. Idles so much better.
yeah, swapping injectors and changing the req fuel to cover for it only sorta works. If you have all the low pw non linear stuff plugged in it probably works better, but for most people, your idle PW doesn't change much from a 600 to say a 1300cc injector. Where it changes a lot is generally past the 2.5ms range. You will likely find that you can reduce your in boost above 2000rpms bins by close to the % difference if not a little more, but down around idle don't expect it to change a whole lot.
 
I run my injectors at 36 psi and at that pressure the flow rate is 515 ml /min. My Req Fuel is 6.4 ms. My estimate is that based upon your Req Fuel of 5.6 ms you have a B23, B230. I am running na with a B20 at 2.02 l. My idle pulse width when the engine is up to operating temperature is around 1.9 - 2 ms at 900 RPM. With that size injector I expect that you are fa; but, operation at idle conditions should be similar. My injector dead times are 0.25 ms at 13.2 volts which means at idle my actual open time is around 1.65 -1.75 ms. If I had 1000 ml/min injectors with your 1.1 ms (approximate at 13.2 volts) ms dead time I would expect my idle PW to be around (515/1000)x1.65 + 1.1 = 1.95 ms to 2.00 ms. I target an AFR of 14.7 at idle. If you target a lower AFR then your PW would be proportionally longer. Your larger engine should also result in a slightly longer idle pulse width. If your voltage is running lower than 13.2 volts that would also increase dead time and the commanded pulse width.

As an observation, I have flow characterized my injectors and I know that at 1 ms commanded pulse widths they have entered an area of non linear operation and are no longer flowing 515 ml/min. I know zip about your 1000 cc injectors; but, as a general observation unless you have the flow curves for the injectors and know that they are linear down to 1 ms or less that is entering an extremely iffy area of operation if the commanded pulse widths are like the 2 ms I calculated. The 700 ml/min injectors would have an idle pulse width that was 43 % longer than the 1000 cc injectors (everything else being equal) which probably put them into a nice safe zone of operation.
 
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My PW with the 700cc's is 3.1ms at idle. It was 4.2ms at idle with the 1000cc's. It drove alright but idled like crap. I bailed on the 1000cc's and put back in the 700cc's. Idles so much better.

That comparison tells you that something is screwy. The longer PW on the 1000 cc injectors says that they are flowing less fuel per min than the 700 cc injectors. The 1000cc injectors might have a very large non linear region of operation.

I am still surprised that your fuel PW, even with consideration of your longer dead time, is so much longer than mine at idle. I am running MSExtra sequential. Are you running batch fire with the alternate squirt? It almost seems like your 700 cc fuel delivery is twice as much per squirt as mine.
 
Ahh yes. I guess specs would help.
B230ft
700cc inj (untimed injection, alternating inj staging,2 squirts per cycle)

Microsquirt
Gt30 (26psi)
Pump gas 93, water meth injection.
I really don't believe that these are 1000CC injectors. Unless my settings are totally off within tunerstudio/ microsquirt.


That comparison tells you that something is screwy. The longer PW on the 1000 cc injectors says that they are flowing less fuel per min than the 700 cc injectors. The 1000cc injectors might have a very large non linear region of operation.

I am still surprised that your fuel PW, even with consideration of your longer dead time, is so much longer than mine at idle. I am running MSExtra sequential. Are you running batch fire with the alternate squirt? It almost seems like your 700 cc fuel delivery is twice as much per squirt as mine.
 
Put the injectors in and start with dead time, and req_fuel calculator, my guess is like 142guy said, it’s not at a linear point where the actual fuel is controllable.
 
I just noticed in your 3 rd post that you referred to these as modified injectors. I don't know how they were modified; but, Injector Dynamics posted an article on their website a couple of years ago that had some fairly negative comments about modifying injectors for higher flow rates. The ID article may or may not be biased (like everything else on the web) so take that under consideration; but, you may want to see if you can find that article and whether any of the issues that they raised may be relevant to your problems.
 
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